This application claims the priority of PCT/EP99/10240 filed Dec. 21, 1999 and German patent document 198 60 2502, filed Dec. 24, 1998, the disclosures of which are expressly incorporated by reference herein.
The present invention relates to a change-speed gearbox with two component transmissions arranged parallel to one another in the power flow.
The manual gearboxes with a friction clutch that predominate in motor vehicles are simple and robust but have the disadvantage that an interruption in the tractive effort occurs during gear changes. Although conventional automatic transmissions with a hydrodynamic converter avoid an interruption in the tractive effort during gear changes, they are less efficient than manual gearboxes owing to the converter. Moreover, they are heavier and more costly.
In the case of change-speed gearboxes with two frictional power-shift clutches and two component transmissions arranged parallel to one another in the power flow, gear changes can be performed under load, and more specifically with overlapping control of the power-shift clutches. This makes it possible to achieve economical automatic transmissions with good efficiency. In general, the even-numbered gears are assigned to one component transmission and the uneven-numbered gears are assigned to the other component transmission, with the result that it is possible to perform sequential gear changes under load but it is not readily possible to skip individual gears, referred to as double upshifting or double downshifting.
U.S. Pat. No. 4,658,663 has disclosed a change-speed gearbox of the generic type. In this change-speed gearbox, an input shaft is connected to an output shaft by a first and a second component transmission, which are arranged parallel to one another in the power flow and each have a frictional power-shift clutch. Concentrically arranged intermediate shafts of the component transmissions can be connected to the input shaft by the power-shift clutches. The intermediate shafts can be operatively connected to the output shaft by means of gearbox constants, of a common layshaft arranged parallel to the input shaft and of gearwheel pairs. The gearwheel pairs for forward gears I, III, and IV and the gearwheel pair for the reverse gear belong to the first component transmission. The fourth gear is designed as a direct gear and can be selected by engaging a selector element between the output shaft and the intermediate shaft of the first component transmission.
The gearwheel pairs of forward gears II and V and an additional gearwheel pair, the transmission ratio of which is equal to the transmission ratio of third gear, the gearwheel pair of which belongs to the first component transmission, belong to the second component transmission. In the first component transmission, a gearwheel clutch for third gear and the direct clutch for fourth gear are combined to give a changing clutch with a common sliding selector sleeve, which can be coupled to a loose wheel of the gearwheel pair for third gear or to the output shaft.
Although all double downshifts and double upshifts are possible without an interruption in torque transmission in this change-speed gearbox, the gear changes from the direct fourth gear to first and third gear, the gearwheel pairs of which likewise belong to the first component transmission, require the temporary engagement of the additional gearwheel pair of third gear. To start off from first gear, the first power-shift clutch of the first component transmission is always used, as a result of which there is increased wear on the latter compared with the second power-shift clutch.
An object on which the invention is based is to develop a change-speed gearbox, in particular to reduce the effort involved in its construction, its costs and weight and increase efficiency. According to the invention, it is achieved by the features of the independent claims. Further refinements will become apparent from the subclaims.
The invention starts from a change-speed gearbox in which an input shaft is connected to an output shaft by at least one first and one second component transmission, which are arranged parallel to one another in the power flow. Each component transmission has a frictional power-shift clutch and an intermediate shaft, it being possible in each case for the intermediate shaft to be operatively connected to the input shaft by means of the power-shift clutch. The change-speed gearbox furthermore has at least one gearbox constant per component transmission, each gearbox constant having a gearwheel on one of the two intermediate shafts, at least one of which gears can be operatively connected to a first layshaft arranged parallel to the input shaft.
It is proposed that at least one gearbox constant can be brought into operative connection with the first and the second power-shift clutch. Power can advantageously be output to a layshaft by both power-shift clutches via at least one gearbox constant. With a certain number of gearwheel pairs, it is possible to achieve a particularly large number of power-shift options and, in particular, to achieve at least the most important double upshifts and double downshifts under load without additional gearwheel pairs. If at least one gearwheel of the gearbox constants on an intermediate shaft is embodied as a loose wheel and can be brought into operative connection with the first power-shift clutch by means of at least one selector element and with the second power-shift clutch by means of a selector element or, preferably, can be connected directly by means of a respective selector element to one intermediate shaft in each case, a gearbox constant can be brought into operative connection with the first and the second power-shift clutch in a manner that is particularly simple in terms of construction and economical in terms of space and with a high efficiency and low losses due to tooth engagements.
Further degrees of freedom with respect to various gear change options can furthermore be achieved if the gearwheel of the first gearbox constant on the first intermediate shaft and the gearwheel of the second gearbox constant on the second intermediate shaft are embodied as loose wheels. It is furthermore possible to achieve a situation where both power-shift clutches can be closed in all gears.
If at least the gearbox constant assigned to the lowest gear can be brought into operative connection with the first and the second power-shift clutch, either the first, the second or both power-shift clutches can advantageously be used for the purpose of starting off. The stresses resulting from the starting-off operation can be distributed between both power-shift clutches. Despite economical dimensioning, it is possible to avoid an excessive temperature, to reduce wear and extend service intervals. If one power-shift clutch fails, the second power-shift clutch can furthermore be used for starting off from first gear and reliability of mobility can be increased.
The power-shift clutches can also be designed differently for different starting-off operations and/or be used individually or jointly for starting off from a higher gear. The power-shift clutches are advantageously used individually or jointly for starting off as a function of at least one operating parameter, e.g. as a function of loading, friction, temperature and/or wear etc. detected at the power-shift clutches.
It is furthermore proposed that the power-shift clutch of the first component transmission can be brought into operative connection with a second layshaft parallel to the input shaft by means of the first gearbox constant, which shaft can be brought into operative connection with the output shaft by at least one gearwheel pair assigned to the first component transmission. An additional torque path can be created by means of the additionally engageable second layshaft. If, in particular, the output shaft can be connected to the intermediate shaft of the first component transmission by an engageable and disengageable selector element to form a direct gear, it is advantageously possible to create three torque paths between the input shaft and the output shaft. The torque paths can be used alternately and, in particular, a double downshift from the direct gear and a double upshift to the direct gear under load are made possible without an additional gearwheel pair.
In a refinement of the invention, it is proposed that the direct gear is the highest gear. Good efficiency can be achieved, in particular, when travelling on ordinary roads and motorways at high speeds. Losses due to tooth engagements can be avoided.
A particularly space-saving change-speed gearbox with a small number of gearwheel pairs and a large number of power-shift options, in particular double upshift and double downshift options under load, can be achieved if the gearbox constants are different from one another and at least one gearbox constant can be brought into operative connection with the output shaft by means of both layshafts. If at least two gearbox constants are operatively connected to each layshaft, each gearwheel pair can particularly advantageously be brought into operative connection with at least two gearbox constants. Each gearwheel pair can be assigned at least two gears or, in the case of more than two gearbox constants, more than two gears.
In various embodiments that may appear appropriate to the person skilled in the art, the gearbox constants can be connected to both layshafts. However, this can be achieved in a particularly space-saving and economical manner with two layshafts that are arranged concentrically to one another and can be operatively connected to one another by a selector element. At the same time, the selector element is advantageously arranged in a space-saving manner at the end of the second layshaft adjacent to the power-shift clutches.
The solution according to the invention, that at least one gearbox constant can be brought into operative connection with both power-shift clutches, and the solution according to the invention, that at least one layshaft can be brought into operative connection with both gearbox constants, each independently contributes to an increase in the power-shift options and in efficiency, to elimination of gearwheel pairs and to allowing not only sequential shifts under load but also double upshifts and double downshifts under load. Although these solutions are employed independently of one another, they are particularly advantageously employed jointly in a change-speed gearbox.
In a refinement, it is proposed that a gearwheel pair assigned to the first component transmission and a gearwheel pair assigned to the second component transmission are assigned to the next-smallest gear to the direct gear, thereby, in particular, making possible double downshifts and double upshifts to and from this gear and load. A double downshift from the next-smallest gear to the direct gear is often required for overtaking and is regarded as an important shifting operation.
The gear change from first to second gear often takes place under a high load. To allow a particularly comfortable gear change, one gearwheel pair is advantageously assigned to the lowest and the second-lowest gear. In a neutral position, the selector elements for the second gear can be preselected, thus making it possible, after starting off from first gear, to change from first to second gear simply by overlapping control of the power-shift clutches.
In another refinement, it is furthermore proposed that the gearwheel pair of the gearwheel pairs assigned to the forward gears is arranged nearest to a shaft mounting for the output shaft in a gearbox casing. Bending of the shafts and wear can be reduced.
In order to achieve close spacing of the shafts and hence a small overall volume of the gearbox and a low weight, one gearwheel for the highest gear is advantageously arranged on the layshaft that has a larger diameter than the other layshaft. The large diameter can advantageously be used for multiplication. Close spacing of the shafts and a low overall volume can furthermore be achieved if selector elements of the component transmissions are arranged in an axially offset manner. An unnecessarily large shaft spacing due to the selector elements can be avoided.
In an advantageous refinement for a wide range of applications, there are, in addition to the two gearbox constants, three gearwheel pairs for six different forward gears and one gearwheel pair for at least one reverse gear. One gearwheel of the gearwheel pair assigned to fourth and sixth gear is arranged on the second layshaft, and one gearwheel of the gearwheel pair assigned to third and fourth gear and one gearwheel of the gearwheel pair assigned to first and second gear are arranged on the first layshaft.
An advantageous variant furthermore comprises arranging one gearwheel of the gearwheel pair assigned to third and sixth gear on the second layshaft and one gearwheel of the gearwheel pair assigned to second and fourth gear and one gearwheel of the gearwheel pair assigned to first and second gear on the first layshaft. It is advantageously possible to achieve progressive graduation of the change-speed gearbox and/or a first gear with a large reduction, e.g. for use in the case of an internal combustion engine with a turbocharger, in the case of an internal combustion engine with a low power and/or in the case of an off-road vehicle etc.
An advantageous graduation of the gears, especially a large difference in the transmission ratio between second and fourth gear and/or with a progressive characteristic can be achieved in a space-saving manner if at least one gearwheel for a fourth gear and one gearwheel for a first and a second gear are arranged on the first layshaft, and at least one gearwheel for a sixth gear and one gearwheel for a third gear are arranged on a second layshaft. In this case, a large number of power-shift options and degrees of freedom for a particular graduation of the gears can be achieved if the gearwheels on the second layshaft for third and sixth gear are each embodied as loose wheels and can be operatively connected to the second layshaft by means of a common selector element. In the case of second to sixth gear, in particular, both power-shift clutches can furthermore be closed. Losses, especially those due to drag torque and wear, especially at a thrust bearing of a crankshaft and a release bearing of the power-shift clutches can be reduced and service life can be extended.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompany in a drawings.